1. Field of the Invention
The invention relates to a molten metal pump component that has tension applied to it so that the component is more resistant to breakage. More particularly, the invention relates to at least one molten metal pump component comprising a tension rod inside a structural refractory outer core material.
2. Description of the Related Art
As used herein, the term “molten metal” means any metal or combination of metals in liquid form, such as aluminum, copper, iron, zinc and alloys thereof. The term “gas” means any gas or combinations of gases, including argon, nitrogen, chlorine, fluorine, Freon, and helium, which can be released into molten metal.
Known pumps for pumping molten metal (also called “molten metal pumps”) include a pump base (also called a housing or casing), one or more inlets, an inlet being an opening to allow molten metal to enter a pump chamber (and is usually an opening in the pump base that communicates with the pump chamber), a pump chamber, which is an open area formed within the pump base, and a discharge, which is a channel or conduit communicating with the pump chamber (in an axial pump the pump chamber and discharge can be the same structure or different areas of the same structure) leading from the pump chamber to the molten metal bath in which the pump base is submerged. A rotor, also called an impeller, is mounted in the pump chamber and is connected to a drive shaft. The drive shaft is typically a motor shaft coupled to a rotor shaft, wherein the motor shaft has two ends, one end being connected to a motor and the other end being coupled to the rotor shaft. The rotor shaft also has two ends, wherein one end is coupled to the motor shaft and the other end is connected to the rotor. Often, the rotor shaft is comprised of graphite, the motor shaft is comprised of steel, and the two are coupled by a coupling, which is usually comprised of steel.
As the motor turns the drive shaft, the drive shaft turns the rotor and the rotor pushes molten metal out of the pump chamber, through the discharge, which can be an axial, tangential or any type of discharge, and into the molten metal bath. Most molten metal pumps are gravity fed, wherein gravity forces molten metal through the inlet (either a top inlet, bottom inlet or both) and into the pump chamber as the rotor pushes molten metal out of the pump chamber.
Molten metal pump casings and rotors usually employ a bearing system comprising ceramic rings wherein there are one or more rings on the rotor that align with rings in the pump chamber (such as rings at the inlet, which is usually at the top of the pump chamber and/or bottom of the pump chamber) when the rotor is placed in the pump chamber. The purpose of the bearing system is to reduce damage to the soft, graphite components, particularly the rotor and pump chamber wall, during pump operation. Known bearing systems are described in U.S. Pat. Nos. 5,203,681, 5,951,243 and 6,093,000 to Cooper, the respective disclosures of which are incorporated herein by reference. Further, U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 4,169,584 to Mangalick, U.S. Pat. No. 5,203,681 to Cooper and U.S. Pat. No. 6,123,523 to Cooper (the disclosure of U.S. Pat. No. 6,123,523 to Cooper is also incorporated herein by reference) all disclose molten metal pumps. U.S. Pat. No. 6,303,074 to Cooper discloses dual-flow rotors and its disclosure is incorporated herein by reference.
Furthermore, U.S. Pat. No. 7,402,276 to Cooper entitled “Pump With Rotating Inlet” (also incorporated by reference) discloses, among other things, a pump having an inlet and rotor structure (or other displacement structure) that rotate together as the pump operates in order to alleviate jamming.
The materials forming the components that contact the molten metal bath should remain relatively stable in the bath. Structural refractory materials, such as graphite or ceramics, that are resistant to disintegration by corrosive attack from the molten metal can be used. As used herein “ceramics” or “ceramic” refers to any oxidized metal (including silicon) or carbon-based material, excluding graphite, capable of being used in the environment of a molten metal bath. “Graphite” means any type of graphite suitable for molten metal pump components, whether or not chemically treated. Graphite is particularly suitable for being formed into pump components because it is (a) relatively soft and easy to machine, (b) not as brittle as ceramics and less prone to breakage, and (c) less expensive than ceramics.
Three basic types of pumps for pumping molten metal, such as molten aluminum, are utilized: circulation pumps, transfer pumps and gas-release pumps, although the present invention could be used with any type of device used in the processing of molten metal. Circulation pumps are used to circulate the molten metal within a bath, thereby generally equalizing the temperature of the molten metal. Most often, circulation pumps are used in a reverbatory furnace having an external well. The well is usually an extension of a charging well where scrap metal is charged (i.e., added).
Transfer pumps are generally used to transfer molten metal from the external well of a reverbatory furnace to a different location such as a ladle or another furnace. Examples of transfer pumps are disclosed in U.S. Pat. No. 6,345,964 B1 to Cooper, the disclosure of which is incorporated herein by reference, and U.S. Pat. No. 5,203,681.
Gas-release pumps, such as gas-transfer pumps, circulate molten metal while releasing a gas into the molten metal. In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen, or dissolved metals, such as magnesium, from the molten metal. As is known by those skilled in the art, the removing of dissolved gas is known as “degassing” while the removal of magnesium is known as “demagging.” Gas-release pumps can be used for either of these purposes or for any other application for which it is desirable to introduce gas into molten metal.
One problem with standard molten metal components, especially elongated ones such as support posts and impeller shafts is that they, are susceptible to breakage, for example, if struck against a hard surface while being moved.